Cell for refining aluminum by fusion electrolysis



June 4, 1968 A. DAURAT 3,386,908

CELL FOR REFINING ALUMINUM BY FUSION ELECTROLYSIS Filed Nov. 27, 1964Fjg.1 PRIOR ART INVENTOR. Anne: 4. 0400/47 79014 M feat A77]!- UnitedStates Patent 3,3863% CELL FOR REFINING ALUMINUM BY FUSION ELECTROLYSISAndr Daurat, Auzat, Ariege, France, assignor to Pechiney, Compagnie deProduits Chimiques et Eicctrometallurgiques, Paris, France Filed Nov.27,1964, Ser. No. 414,140

Claims priority, application France, Dec. 3, 1963, 95 ,021 7 Claims.(Cl. 204-243) ABSTRACT OF THE DISCLOSURE A cell for the electrolyticrefining of aluminum which comprises an enclosure of refractory materialhaving an access opening at the top and a cover dimensioned to span theaccess opening formed of a first stationary portion which is fixed tothe housing and a movable portion which is adapted to be received infitting relationship in an opening defined by the fixed stationaryportion, an anodic sole plate at the bottom of the enclosure having anelectrical connection, an anode layer of aluminum alloy to be refinedoverlying the anodic sole plate layer, a layer of electrolytic liquoroverlying the anode layer, a cathode layer of refined metalsubstantially of frusto-conical shape having the base portion of largercross-sectional dimension at the bottom in contact with the electrolyticliquor and an upper exposed portion of lesser dimension, and a cathodein contact with the cathode layer having an electrical lead extendingthrough the housing into contact with the cathode layer.

This invention relates to the production of aluminum and moreparticularly to a new and improved novel cell for the refining ofaluminum by fusion electrolysisf It is well known that cells for fusionelectrolysis used for refining aluminum electrolytically generallycomprise a conductive soleplate incontact with a soluble anode layer ofa metal in the form of an 'alloy of themetal to be refined underlying alayer of electrolytic liquor which is disposed between the anode and acathode in the form of another metallic layer consisting of the refinedaluminum.

Since the final result of the electrolytic operation is selectivetransference of aluminum from the alloy of the anode to the metal of thecathode which, as stated above, is composed of the refined metal, thepolarization voltage is only a very small fraction of the total voltageat the terminals of the cell. When the cell is in operation, theelectric power absorbed is substantially equal to the heat losses. Itis, therefore, desirable to seek to reduce these losses to a minimum soas to decrease the energy consumption per ton of refined metal. Somereduction may be achieved by thermal insulation of the cell about itsbottom and side walls and by providing a hood to cover the upper surfacebut such usage results in the elimination of conventional suspendedelectrodes.

The French Patent No. 970,508, granted on June 21, 1956, describes anelectrolytic cell for refining aluminum by the process which makes useof three superimposed layers including two conductive soleplates whichare arranged at different levels and electrically insulated one from theother and separated by impervious brickwork made of appropriatematerials and in contact with an end portion of one of the metalliclayers with the soleplates acting as current carriers.

This type of cell has a number of disadvantages. One

Patented June 4, 1968 of the main objections is that the brickworkseparating the soleplates tends to deteriorate rapidly because of theseepage therethrough of electrolytic liquor thereby shortening the lifeof the cell. Another serious objection is that the useful section of thecell is small for equivalent production and therefore calls for anincrease in the cost of the cell and the space required to be madeavailable.

It is an object of this invention to produce a cell for fusionelectrolysis in the refining of aluminum in which the cell ischaracterize-d by high yield and it is a related object to produce acell of the type described for the electrolytic refining of aluminum inwhich the cell is characterized by a long useful life and a working areaof large dimension for greater efficiency.

' These and other objects and advantages of this invention willhereinafter appear and for purposes of illustration, but not oflimitation, embodiments of the invention are shown in the accompanyingdrawing, in which:

FIG. 1 is a schematic sectional elevational view of a cell embodying theconstruction heretofore employed for fusion electrolysis;

FIG. 2 is a schematic sectional elevational view of a cell embodying thefeatures of this invention for fusion electrolysis in the refining ofaluminum; and

FIG. 3 is a schematic sectional elevational view similar to that of FIG.2 showing a modification in the fusion electrolysis cell.

Briefly, described, a cell embodying the features of this invention forhigh yield fusion electrolysis in the refining of aluminum and which ischaracterized by a long useful life and maximum working area comprises acell having a cover which at least partially extends over a bath ofrefractory material; an anode formed of the alloy tobe refined incontact with an anodic soleplate in the bottom of the bath and having atleast one current input lead which passes upwardly through the bath; anda cathode formed of the metal which is refined in contact with at leastone cathodic electrode having at least one current input lead whichpasses downwardly through the bath and which is suspended from the upperportion of the masonry.

In a special embodiment of the invention, the electrolytic cell furthercomprises at least one of the additional features, namelythe bath ispartially closed at its upper portion by a cover which is integral withthe masonry of the bath and which contains an aperture sealed by amovable portion of the cover from which the cathodic electrode issuspended and in which the bath is closed in its upper portion by acover comprising a stationary part integral with the masonry of the bathand from which the cathodic electrode is suspended and a movable portionthrough which access can be gained to the interior.

With reference now to the drawing, illustration is made of a bath 10(5%) in FIG. 2) in FIG. 3) of insulating brick separated from the liquorby a lining in the form of a brickwork 11 (51 in FIG. 2) (71 in FIG. 3)of anticorrosive material. At the lower end of the space defined by thebrickwork 11 is the anodic conductive soleplate 12 (52 in FIG. 2) (72 inFIG. 3) underlying the layer 15 (55 in FIG. 2) (75 in FIG. 3) of thealloy to be refined which in turn underlies the layer 16 (56 in FIG. 2)(76 in FIG. 3) of the electrolytic liquor. The latter is in turn coveredby a layer 17 ('57 in FIG. 2) (77 in FIG. 3) of refined metal whichfunctions as the cathode. The current reaches the :anodic soleplatethrough lead 18 (58 in FIG. 2) (78 in FIG. 3). In the standard cell ofFIG. 1, the cathodic layer 17 of refined meal communicates at one endwith a soleplate 13 which rests on the insulating brickwork 10 and isconfined between the anti-corrosive linings 11. The lead 19 extendsupwardly through the brickwork 10 into electrical contact with thesoleplate 13.

The removable cover 14 extends across the upper portion of the cell tominimize heat loss from the bath in the upward direction.

The anodic alloy to be refined is supplied to the layer 15 (55 in FIG.2) (75 in FIG. 3) through insulated pits 20 (60 in FIG. 2) (80 in FIG.3) arranged in laterally spaced apart relation in the brickwork for goodheat insulation, with each pit being provided with a removable lid 21(61 in FIG. 2) ('81 in FIG. 3) over the inlet.

In FIG. 1, the refined aluminum is removed from the layer 17 by asuction tube operating through the top of the cell, either through anopening provided in the cover 14, which may or may not be provided witha sealing lid, or through the wide opening, when the cover is removed.

This arrangement has a number of disadvantages:

(1) The liquor 16 seeps into the anti-corrosive brickwork 11 and oftenoperates to bring the liquor 16 into direct contact with the cathodicsoleplate 13 and its lead 19 with the result that a large amount ofenergy is lost and the cell rapidly becomes inoperative;

(2) The alloy 15 may also seep into the brickwork 11 to cause ashort-circuit between the anodic alloy 15 and the cathodic soleplate 13with its lead 19;

(3) The working section of the bath, defined by the electrolytic liquor16, is of small cross-section as compared to the total cross-section ofthe cell thereby to increase the cost of the bath and the amount ofspace required per unit volume of production;

(4) Consumption of electrolytic liquor 16 increases in proportion to thearea of contact between the refined metal 17 and the atmosphere and, aswill be seen, this area is far greater than the useful section therebyto introduce undesirable inefiiciencies;

The area of the cover is very large in relation to the useful section ofthe bath thereby to expose a substantial area to heat loss and the coverof larger dimension is more expensive and clifficult to operate.

In accordance with the practice of this invention, the cells shown inFIGS. 2 and 3 differ essentially from that of FIG. 1 in that instead ofmaking use of a cathodic soleplate 13, use is made of a suspendedelectrode 53 in FIG. 2 and 73 in FIG. 3 with the leads 59 and 79extending through the upper portion of the housing and fixed to someportions thereof to permit complete hooding.

In the cell of FIG. 2, use is made of a two-part cover in which one part54 is fixed to form an integral part of the masonry 50 of the bath andwhich is formed with an access opening at the top of specific dimension.The other part 63 is a movable member in the form of a lid having alower portion which is dimensioned to be received in fittingrelationship within the opening and an upper portion of larger dimensionthan the opening to extend beyond the edge portions of the fixed portionso as to rest upon the portions of the stationary cover adjacent theopening when the portion of smaller dimension is received within theopening to seal the opening. The cathode electrode 53 is suspended fromthe stationary portion 54 of the cover and the lead 59, for currentinput, passes through said cover portion.

In the cell shown in FIG. 3, the cover again comprises a stationaryportion 74 fixed to form an integral part of the masonry 70 of the bathand it is also formed with an opening therethrough for gaining access tothe interior of the bath. The other portion 83 comprises a movablemember similar to that described with reference to the lid 63 of FIG. 2.The cathode electrode 73 is suspended from the movable portion of thecover with the lead 79 extending therethrough.

With this construction, it is possible to arrange the cell with thecathode layer 57 dimensioned to span the entire bath for maximum area ofcontact with underlying layer 56 of electrolytic liquor and with theupper end portion of the cathode layer of lesser dimension toaccommodate the cathode 53 alongside thereof without increasin thedimension of the bath. For this purpose, as shown in FIGS. 2 and 3, thecathode layer 57 and 77 is formed of a base portion of maximumcrossseotion with a portion of frusto-conical shape in an intermediateportion, as shown in FIG. 2, or in an upper end portion, as shown inFIG. 3, to form the upper portion of lesser dimension than the baseportion to accommodate the cathode 53 alongside the upper portion of thecathode layer of smaller dimension, as shown in FIG. 2, or for contactwith the central portion of the cathode layer, when suspended from themovable lid, as shown in FIG. 3.

This novel arrangement obviates many of the disadvantages of the presentcell as outlined above and as hereinafter briefly outlined:

(1) Attack on the brickwork 51 or 71 no longer remains as a problemsince the brickwork has no point of weakness on the level of the liquor;

(2) Short-circuiting between the anodic alloy 52 or '72 and the cathodicelectrode 53 or 73 will no longer occur since the electrodes and theircorresponding leads are not at a level corresponding to that of thealloy;

(3) The useful section of the cell is markedly increased by comparisonwith thearrangement of FIG. 1 thereby to provide for a considerablereduction in the cost of insulation and in the amount of space requiredfor the cell;

(4) The area of contact between the refined metal 57 or 77 and the airis less than that of the useful section thereby correspondingly toreduce the consumption of electrolytic liquor;

(5) The area of the access opening through the cover is markedlyreduced;

(6) In the event of need for replacement of a graphite electrode forreasons of combustion, repair or exchange, access to the electrode canbe had more easily and at less expense with cells of the typeillustrated in FIGS. 2 and 3.

It will be apparent from the foregoing that the cell of this inventionobviates the disadvantages experienced with cells of the type presentlyemployed and at the same time permits integral hooding which isimportant to the achievement of high yields.

It will be understood that changes may be made in the details ofconstruction, arrangement and operation, without departing from thespirit of the invention, especially as defined in the following claims.

I claim:

1. A cell for the electrolytic refining of aluminum comprising anenclosure of refractory material having an access opening at the top anda cover dimensioned to span the access opening formed of a firststationary portion fixed to the housing and having an access openingtherethrough and a second movable portion adapted to be received infitting relationship within said opening, an anodic soleplate at thebottom of the enclosure and an electrical lead extending upwardlythrough the enclosure into contact with the soleplate, an anode layer ofaluminum alloy to be refined on the upper surface of the anodicsoleplate, a cathode layer formed of the refined metal of greatercross-sectional dimension at the bottom portion and lesser dimension atits upper portion, a cathode in contact with the cathode layer and anelectrical lead extending downwardly through the housing into contactwith the anode, and a layer of electrolytic liquor in communicationbetween the cathode layer and the anode layer, the cathode beingsuspended from the upper portion of the enclosure.

2. A cell as claimed in claim 1 in which the cathode is suspended fromthe movable lid.

3. A cell as claimed in claim 1 in which the cathode is suspended fromthe fixed portion of the cover.

4. A cell as claimed in claim 1 in which the cathode layer and the layerof electrolytic liquor are each of maximum dimension at their interface.

8,386, 908 5 6 5. A cell as claimed in claim 1 in which the cathode vReferences Cited is positioned alongside a portion of the cathode layer.P A NT 6. A cell as claimed in claim 5 in which the cathode UNITEDSTATES TE S is positioned alongside the upper portion of the cathode 2 gg g layer offset inwardly from the enclosure to maximize 5 22455O56/1941 2o4 67 the cross-section of the layer below the cathode. 16 en op7. fi cell as claimed in claim 1 in which the cathode JOHN H. M ACKPrimary Examiner. 1s positloned alongside the upper portion of lesserdi- I mension and in an area which does not extend beyond the HOWARDWILLIAMS Examine base portion of larger dimension. 10 D. R. VALENTINE,Assistant Examiner.

